The present invention relates to a magnetic disk drive (HDD) and particularly to a reproduction control method for avoiding deterioration of drive performance caused by application of coefficient learning in a state in which the positional divergence of a read head is large.
The configuration and reproducing operation of a background-art magnetic disk drive will be described below.
FIG. 12 shows an example of the configuration of a magnetic disk drive (HDD) 10.
The HDD 10 comprises a head disk assembly (HDA) 20, and a packaged circuit board (PCB) 30.
The HDA 20 includes magnetic disks 2-1 to 2-5, suspension 108 provided with magnetic heads 1-1 to 1-10 attached thereto, a carriage 103, a read/write IC (R/WIC) 104 attached on the carriage 103, a spindle motor 105, and a flexible printed cable (FPC) 106.
The PCB 30 is constituted by a signal processing LSI (SPC) 21, a hard disk controller chip (HDC) 22, a servo controller (SRVC) 23, a micro-processor (MP) 24, a host bus interface chip (HBI) 25, an ROM 26, a buffer RAM 27, etc.
The read operation of the HDD 10 will be described below with reference to FIGS. 12 through 15.
A read signal corresponding to a magnetic field and detected from the magnetic disk 2-1 by an MR (Magneto-Resistive) head of the magnetic head 1-1 in FIG. 12 is supplied to the R/WIC 104 through wiring on the suspension 108.
In the R/WIC 104, selection of one of the magnetic heads 1-1 to 1-10 and the sense current value of the selected MR head are set in advance through the MP 24.
A resistance change of the MR head due to the magnetic field in the magnetic disk 2-1 is converted into a voltage change. Further, the R/WIC 104 amplifies the read signal to a value of from the order of tens of mVp-p to the order of hundreds of mvp-p and outputs the amplified read signal 33 to the SPC 21.
T his signal 33 is supplied to a read signal processing circuit (RSPC) 201 of the SPC 21 in FIG. 13.
FIG. 14 shows the configuration of the RSPC 201.
The signal 33 is amplified to have a suitable amplitude by a variable gain amplifier (VGA) 210 in the first stage of the RSPC 201. Unnecessary high-frequency noise is removed from the amplified signal and the read waveform of the amplified signal is roughly equalized by an active equalizer (AF) 211.
Then, the analog signal of the AF 211 is converted into a digital signal by an A/D converter (ADC) 212. The digital signal is equalized accurately by a digital equalizer (FIR) 213 in the latter stage.
Further, the signal of the FIR 213 is detected to a row of serial data by a maximum likelihood detector (ML) 214. A sync byte (SB) indicating the start of user data is detected in this serial data row by a sync byte detector (SBDET) 215.
On the basis of a result of the detection, the serial data row is converted into parallel data and decoded by a decoder (DEC) 216. Further, the parallel data is restored to data 34 through a descrambler (DSC) 217. Further, read data 35 is supplied to the HDC 22 through an interface (INT) 202 in FIG. 13.
Further, the data 35 supplied to the HDC 22 is subjected to error detection and error correction by an error correction circuit (ECC) 22-1 in the HDC 22, and supplied as data 48 to a user (host PC, or the like) through the HBI 25.
A control operation will be described below in the case where a cylinder is sought from Cn to Cm to read a plurality of data sectors DS1, DS2, DS3 . . . as shown in FIG. 15.
TRK_WDTH shows an arrangement of servo and data regions.
The servo controller (SRVC) 23 successively reproduces servo signals SRVi recorded on a disk surface to thereby obtain a positioning signal 42 through a servo signal processing circuit (SSPC) 204 to thereby perform positioning control.
The MP 24 gives a seek command (SEEK) 40 to the SRVC 23. The SRVC 23 analyzes the positioning signal 42 obtained in a signal SRV1 (FIG. 13) in servo region. If a judgment is made from the analysis that data is enabled to read, the SRVC 23 outputs a xe2x80x9cread seek completexe2x80x9d signal (RD_SK_COMP) 47 to the HDC 22. As a result, the HDC 22 outputs a xe2x80x9cread gatexe2x80x9d signal (RG) 36 from the data region DS1.
The threshold value of completion of positioning for issuing the RD_SK_COMP 47 in the read operation is generally set to be larger than the threshold value in the write operation to attain reduction of the seek completion time.
At read time, as shown in FIG. 14, the RG 37 supplied to the RSPC 201 through the INT 202 operates most of portions in the RSPC 201 and also operates a coefficient learning circuit (ADAPT) 218 which adaptively learns the coefficient of the FIR 213.
As a result, the coefficient value registered in an equalizing characteristic setting register (COEF) 219 is consecutively changed to a coefficient value for giving good reproducing characteristic even in the case where the resolving power of the reproductive signal 33 varies in accordance with the change of head/disk characteristic, head spacing, or the like, caused by the change of the operating environment, such as temperature, atmospheric pressure, or the like, of the HDD 10.
In such a background art, however, there were two problems as follows.
The first problem is increase of error caused by divergence occurs in the equalizing coefficient of the FIR 213.
As shown in FIG. 15, the effective track width (TRK_WDTH) varies in accordance with the positional divergence of the MR head and the positioning state at write time. Particularly just after seeking, there is the possibility that the positional divergence is widened because of the influence of settling of head, or the like.
When, for example, a data sector DS1 to be read is present just after the RD_SK_COMP 47, the read gate (RG) 37 is opened in the position of DS1 in the condition in which the sufficiently effective track width cannot be obtained because of the aforementioned deterioration, or the like.
In this condition, the ADAPT 218 cannot operate normally. As a result, the initial value Km(init) of the coefficient value of the FIR 213 registered in the equalizing characteristic setting register (COEF) 219 may diverge to a coefficient value Km(adapt) in which data reproduction cannot be performed normally on the basis of a learning operation.
In this case, the data row produced from the NRZ data 34 contains a lot of channel byte errors as shown in FIG. 15. Accordingly, there is a high possibility that the errors cannot be perfectly corrected by the error correction circuit (ECC) 22-1 in the HDC 22.
Further, if the performance for checking the miscorrection of the ECC is insufficient, the possibility that the erroneously corrected data may be sent to the host becomes high (mischecking).
Because the data sector DS2 following the data sector DS1 also uses the aforementioned abnormal coefficient value as an initial value, there is a high possibility that the same problem as described above occurs consecutively.
The data sectors DS3 . . . following the data sector DS2 form a (substantially on-track) sector region having a large effective track width. Also in the sectors DS3 . . . , there is a very high possibility that channel byte error occur frequently.
To correct this error, it is necessary to restart a read operation with the effective track width kept sufficient while rotating the disk to wait for the same sectors (DS1 . . . ) to come in the condition in which the COEF is reset to the initial value Km(init) in a data restoration sequence (retry).
If the aforementioned condition occurs frequently, the performance of the device is lowered greatly.
The second problem is that reproducing characteristic at ordinary time deteriorates.
In the background art shown in FIG. 14, the xe2x80x9cread gatexe2x80x9d signal (RG) is used as a signal for starting the ADAPT 218. Accordingly, in the read state, the coefficient of the FIR 213 registered in the COEF 219 always varies, so that adaptive noise is generated.
In this case, the generation of adaptive noise can be suppressed to thereby avoid the increase of output noise of the FIR 213 if not only the number of bits in the COEF 219 is set to be sufficiently larger than the number of bits in the output of the ADC 212 but also a coefficient-correction step parameter of the ADAPT 218 is set to be sufficiently small.
When the initial coefficient value is out of the optimum coefficient value because of an environmental change, or the like, there is, however, a tendency that error occurs in a sector of a read leading portion.
That is, the frequency of retries increases if a large environmental change occurs.
To cover the deterioration of the drive performance, specifications of the drive concerning environmental changes, such as head/disk characteristic, spacing between heads/disks, or the like, cannot but be set severely. Accordingly, this brings about both reduction of the yield of heads/disks and increase of the cost of the drive.
An object of the present invention is to solve the aforementioned problems, and to provide a high-performance low-cost magnetic disk drive in which the adaptability of the magnetic disk drive to read signal processing is enhanced so that the frequency of retries or miscorrections is reduced.
In order to achieve the foregoing object, according to an aspect of the present invention, there is provided a magnetic disk drive having a waveform equalization means for equalizing waveforms reproduced, and an adaptive learning means for adaptively learning the equalizing characteristic of the waveform equalization means, wherein the magnetic disk drive further has an abnormal learning detection means for detecting an abnormal operation in the adaptive learning of the equalizing characteristic just after learning of a sector, and an equalizing characteristic resetting means for resetting the equalizing characteristic before the adaptive learning to an initial value before learning of a next sector when abnormality occurs in the adaptive learning, and wherein the adaptive learning of the equalizing characteristic is performed simultaneously with an operation of reproducing designated data.
According to another aspect of the present invention, there is provided a magnetic disk drive having a waveform equalization means for equalizing waveforms reproduced, and an adaptive learning means for adaptively learning the equalizing characteristic of the waveform equalization means, wherein the magnetic disk drive further has an abnormal learning detection means for detecting an abnormal operation in the adaptive learning of the equalizing characteristic just after learning of a sector, and an equalizing characteristic resetting means for resetting the equalizing characteristic before the adaptive learning to an initial value before learning of a next sector when abnormality occurs in the adaptive learning, and wherein the adaptive learning of the equalizing characteristic is performed before an operation of reproducing designated data.
Preferably, the equalizing characteristic of the waveform equalizing means is fixed during the operation of reproducing the designated data.
According to a further aspect of the present invention, there is provided a magnetic disk drive having an active filter supplied with a read waveform of a magnetic disk, an A/D conversion means supplied with an output of the active filter, and a waveform equalizing means supplied with an output of the A/D conversion means, wherein the magnetic disk drive further has: an adaptive learning means for adaptively learning the boost characteristic of the active filter on the basis of the input and output of the waveform equalizing means so that error in the waveform equalizing means is minimized; an abnormal learning detection means for detecting an abnormal operation in adaptive learning of the boost characteristic just after learning of a sector; and a boost characteristic resetting means for resetting the boost characteristic before the adaptive learning to an initial value before adaptive learning of the next sector when abnormality occurs in adaptive learning; and wherein the adaptive learning of the boost characteristic is carried out simultaneously with the operation of reproducing the designated data.
According to a further aspect of the present invention, there is provided a magnetic disk drive having an active filter supplied with a read waveform of a magnetic disk, an A/D conversion means supplied with an output of the active filter, and a waveform equalizing means supplied with an output of the A/D conversion means, wherein the magnetic disk drive further has: an adaptive learning means for adaptively learning the boost characteristic of the active filter on the basis of the input and output of the waveform equalizing means so that error in the waveform equalizing means is minimized; an abnormal learning detection means for detecting an abnormal operation in adaptive learning of the boost characteristic just after learning of a sector; and a boost characteristic resetting means for resetting the boost characteristic before the adaptive learning to an initial value before adaptive learning of the next sector when abnormality occurs in adaptive learning; and wherein the adaptive learning of the boost characteristic is carried out before the operation of reproducing the designated data.
Preferably, the abnormal learning detection means for detecting an abnormal operation in the adaptive learning of the equalizing characteristic just after learning of a sector compares an integrated value of squares of equalization errors of the waveform equalization means with an error threshold value to thereby detect an abnormal operation.
Preferably, the magnetic disk drive further has a maximum likelihood detecting means for most likely detecting a read waveform, wherein the abnormal learning detection means for detecting an abnormal operation in adaptive learning of the equalizing characteristic just after learning of a sector uses a difference metric value between path metric values of the maximum likelihood detecting means as data to be used for detecting the abnormal operation.
Preferably, the read waveform decoding means has an error detection means, wherein the abnormal learning detection means for detecting abnormality in adaptive learning of the equalizing characteristic just after learning of a sector judges an abnormal operation on the basis of a result of detection obtained by the error detection means.
According to a further aspect of the present invention, there is provided a signal processing chip used in a magnetic disk drive for controlling read/write data of a magnetic disk, having: a waveform equalizing means for equalizing a reproductive waveform; an adaptive learning means for adaptively learning the equalizing characteristic of the waveform equalizing means; a quality judgment means for judging the quality of an output signal of the waveform equalizing means; and a function of discarding a result of learning obtained by the adaptive learning means in accordance with a result of judgment obtained by the quality judgment means.
According to a further aspect of the present invention, there is provided a magnetic disk drive having a digital waveform processing means capable of continuously reproducing a plurality of sectors, wherein the magnetic disk drive further has: a sampled data holding means for holding a row of digital sampled data corresponding to at least one sector in a front stage of a waveform equalizing means contained in the digital waveform processing means; and an abnormal sector detection means for detecting abnormality in an output signal of the digital waveform processing means whenever a sector is read; and wherein, when the abnormal sector detection means detects abnormality in an output signal of the digital waveform processing means, the sampled data holding means holds a row of digital sampled data having the detected abnormality so that an abnormal sector is enabled to be decoded again by use of the data row held by the sampled data holding means.
Preferably, the adaptation speed of adaptive learning of the equalizing characteristic during an operation of read data is set to be lower than the adaptation speed of adaptive learning of the equalizing characteristic carried out before the data reproducing operation.